As the size of a semiconductor has been decreased in recent years, there has been a demand for a technology that is used to form shallow bonding. A method of implanting ions of various conductive impurities such as boron (B), phosphorus (P), and arsenic (As) into the surface of a semiconductor substrate used as a solid base substance with low energy has been widely used in a method of manufacturing a semiconductor in the related art.
Although it is possible to form shallow bonding by using the method of implanting ions, there is a limitation on depth of bonding that can be formed by ion implantation. For example, it is difficult to dope a boron impurity at a small thickness, and the depth of the doped region is limited to about 10 nm from the surface of the base substance in the ion implantation.
For this reason, various doping methods have been proposed as a method of forming shallow bonding in recent years. A plasma doping technology of the various doping methods comes into the spotlight as a technology suitable for practical application. The plasma doping is a technology in which reaction gas containing impurities to be doped is plasma-excited and plasma is radiated on the surface of the solid base substance so as to dope the impurities. Further, after the impurities are doped, an annealing process is performed so as to activate the doped impurities.
In general, a light source capable of emitting electromagnetic waves, such as visual light, infrared light, and ultraviolet light, in the wide wave length band is used in the annealing process. However, since the light reflection is high on the surface of the substrate, there are problems that the light absorptance of an impurity doped layer is low and the activation efficiency is low.
In recent years, the following method has been proposed (for example, Patent Document 1). According to the method, Ge ions are implanted into a semiconductor substrate so that the semiconductor substrate is changed to have pre-amorphous structure. Then, impurities are doped by ion implantation, and an absorption layer having a high light absorption coefficient is formed thereon. Further, an oxide layer is firmed as a part of the absorption layer so as to adjust reflectance.
Patent Document 1: U.S. Pat. No. 6,303,476
The above-mentioned method is a method that is performed on the ion implanted layer. An oxide layer was formed to reduce the reflectance. However, large energy needs to be radiated in an annealing process to reduce the sheet resistance. In particular, since laser radiation area per one laser radiation is small in a laser annealing, there is a problem that it is difficult to reduce the sheet resistance. In particular, when an impurity doped depth is reduced to form shallow bonding, or when a shallower contact is formed in bonding, carrier density is increased to improve activation efficiency by annealing. For this reason, large energy is needed. As a result, since the diffusion length of the impurities is increased, it is difficult to finely form a shallow impurity doped region.